The present disclosure relates to a fixing unit and an image forming apparatus provided with the same.
Conventionally, considerable attention has been attracted by a fixing unit in an imaging forming apparatus that uses a rotary belt enabling a reduction in the heat capacity. Furthermore, in recent years, considerable attention has been directed to an induction heating method (IH) for high-speed heating or high-efficiency heating.
A fixing unit using an induction heating method may be associated with a technique, for suppressing an excessive increase in the temperature in a region (non-paper passing region, second region) on the outer side of the paper passing region (first region) in which the sheet of paper is conveyed in response to the width (width of the sheet of paper in a direction vertical to the direction of conveyance of the paper: paper passing width) of the sheet of paper (transfer material) that is conveyed (passes) in the fixing unit, in which the heating amount of a heating rotor in the paper passing region and the non-paper passing region is adjusted.
A fixing unit using an induction heating method includes a heating rotor, a pressure rotor, an induction coil generating a magnetic flux for heat generation by a heating rotor, and a magnetic core portion formed from a magnetic material to thereby reduce the magnetic permeability when temperature of the magnetic core portion reaches a Curie point.
A fixing unit provided with a magnetic core portion to reduce the magnetic permeability when the temperature of the magnetic core portion reaches a Curie point as described above reduces the magnetic permeability of the magnetic core portion when the temperature of the magnetic core portion is higher than or equal to the Curie point in the non-paper passing region of the heating rotor in which no passage of paper has caused a temperature increase. In this manner, excessive temperature increase can be suppressed in the heating rotor.
However, in comparison to use of a magnetic flux shielding member or a degaussing coil for reduction or shielding of the magnetic flux generated in the induction coil, the heating rotor of a fixing unit provided with a magnetic core portion formed from a magnetic material to thereby reduce the magnetic permeability when temperature of the magnetic core portion reaches a Curie point may exhibit a temperature increase in a non-paper passing region. Consequently, there is a need for a fixing unit exhibiting enhanced suppression of excessive temperature increase in a heating rotor.
The present disclosure has the object of providing a fixing unit including a magnetic core portion and enabling enhanced suppression of excessive temperature increase in a heating rotor. It is a further object of the present disclosure to provide an image forming apparatus that includes the fixing unit.